1. Field of the Invention
The present invention relates to a conveying apparatus that uses a hand of a robot for gripping and conveying a workpiece.
2. Description of the Related Art
For a system gripping a workpiece with a robot hand and conveying it to the next process, it is very important to check whether the workpiece is accurately gripped or not. If the hand of the robot has a gripping error, it is necessary to give corresponding redundancy to the system for the next process. In some cases, expansion of the system, such as addition of space or peripheral equipments, is required. For these reasons, attempts have hitherto been made to use a visual sensor to check the state where a workpiece is gripped. In this case, generally, the movement of the robot is interrupted at a position where a characteristic portion of the workpiece is within the visual field of a camera so as to allow the camera to capture an image at a definite time, and then an image is captured by the camera and the gripped state is measured.
Furthermore, a visual sensor is used for measuring the position of a workpiece without stopping a conveying apparatus. This system is called a visual tracking system. With this system, the visual sensor detects a workpiece placed on a belt conveyor acting as a conveying apparatus, the position of the robot is corrected on the basis of the positional deviation of the workpiece on the conveyor, and then the workpiece is taken out by the robot. An example of this visual tracking system is disclosed in Japanese Patent Application Laid-Open No. 8-63214.
If the robot is stopped to observe the gripped state, tact time increases correspondingly, in some cases, to a level unacceptable to users. Furthermore, visual tracking will allow only small-sized workpieces to be processed owing to condition of conveyor size. For example, for large-sized workpieces such as floor panels of automobiles, it is unpractical to incorporate a tracking system using a conveyor, in view of the cost of and the space for the exclusive conveyor.